Naphthalene (NA) is a ubiquitous pollutant to which humans are widely exposed. NA causes tumors in rats and mice, and has been classified as a Possible Human Carcinogen. The mechanism of NA carcinogenicity is believed to involve repeated cycles of NA-induced acute lung injury and repair. A prerequisite for NA cytotoxicity is its bioactivation by cytochrome P450 (CYP) enzymes; the reactive metabolites formed, which derive from the NA-epoxide (NA-O), can deplete cellular glutathione (GSH) and, at higher concentrations, bind covalently to tissue proteins. NA-O can be produced by both lung and liver. The major enzymes responsible for NA bioactivation in the mouse include CYP2A5 and CYP2F2; Cyp2f2-null mice are highly resistant to NA lung toxicity, whereas Cyp2a5-null mice are partially protected against NA nasal toxicity. Both human lung and human liver are capable of metabolizing NA, although large interindividual variations exist in the rates of microsomal NA metabolism and bioactivation. However, the roles of human CYP2A13 and CYP2F1 (orthologs of mouse CYP2A5 and CYP2F2, respectively) in NA bioactivation are not well understood, and the potential impact of variations in hepatic P450 function on an individual's risks of developing NA- mediated lung toxicity remains undefined. The objectives of this application are to define the role of CYP2A13 and CYP2F1 in NA bioactivation and toxicity in the lungs of CYP2A13/2F1-humanized mice; identify human lung regions that are enriched in CYP2A13/2F1 expression; and determine whether P450- mediated NA bioactivation and/or detoxification in the liver could contribute to, or otherwise influence, NA lung toxicity. The central hypothesis is that NA has the potential to cause lung toxicity in humans and that the metabolism of NA in both lung and liver influence the outcome on an individual basis. This hypothesis will be tested in two specific aims that will 1) define the role of CYP2A13 and CYP2F1 in NA bioactivation and toxicity in the lung; 2) define whether hepatic NA metabolism could influence the risks of NA lung toxicity. We will employ a combination of in vivo and in vitro approaches, and utilize a number of genetically modified mouse models, as well as human tissues and cells, to address the specific aims. The long-term goal of these studies is to define the metabolic mechanisms that influence NA-mediated lung toxicity in experimental animals and humans.